filer: fix mysql2 SQL template

weed/command/scaffold/filer.toml

@@ -66,7 +66,7 @@ upsertQuery = """INSERT INTO `%s` (dirhash,name,directory,meta) VALUES(?,?,?,?)
 [mysql2]  # or memsql, tidb
 enabled = false
 createTable = """
-  CREATE TABLE IF NOT EXISTS ` + "`%s`" + ` (
+  CREATE TABLE IF NOT EXISTS `%s` (
     dirhash BIGINT,
     name VARCHAR(1000) BINARY,
     directory TEXT BINARY,